qom: reverse order of instance_post_init calls

Currently, the instance_post_init calls are performed from the leaf
class and all the way up to Object.  This is incorrect because the
leaf class cannot observe property values applied by the superclasses;
for example, a compat property will be set on a device *after*
the class's post_init callback has run.

In particular this makes it impossible for implementations of
accel_cpu_instance_init() to operate based on the actual values of
the properties, though it seems that cxl_dsp_instance_post_init and
rp_instance_post_init might have similar issues.

Follow instead the same order as instance_init, starting with Object
and running the child class's instance_post_init after the parent.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qom/object.h

@@ -445,7 +445,8 @@ struct Object
  *   class will have already been initialized so the type is only responsible
  *   for initializing its own members.
  * @instance_post_init: This function is called to finish initialization of
- *   an object, after all @instance_init functions were called.
+ *   an object, after all @instance_init functions were called, as well as
+ *   @instance_post_init functions for the parent classes.
  * @instance_finalize: This function is called during object destruction.  This
  *   is called before the parent @instance_finalize function has been called.
  *   An object should only free the members that are unique to its type in this